This invention relates in general to acoustical partitions and in particular to modular (movable) acoustical wall panels for use in office environments. There are several basic design properties such as appearance, feel, rigidity (or structural integrity) and noise abatement which manufacturers of acoustical partitions attempt to provide in the design and construction of their products. Very often a high-density fiberglass material is placed inside of a rigid outer frame and both are covered with a decorative fabric. As one design variation, the fiberglass may have either a soft (low-density) outer layer or a rigid, tackable outer layer placed over both sides of the frame prior to covering the assembly with a decorative outer fabric (cover). It is also common for these somewhat typical partitions to have a rigid septum of steel, paperboard, fiberboard or wood sandwiched between two layers of fiberglass. This sandwich (lamination) may be placed inside of the rigid outer frame in place of a single high-density fiberglass layer.
Most of the foregoing partition assembly concepts rely on either the high-density fiberglass or the sandwiched construction to provide both rigidity and noise abatement properties. However, high-density fiberglass is extremely expensive compared to lower-density fiberglass material and the higher-density material may offer little or no increase in noise abatement properties. Since one of the more significant design properties of acoustical partitions is the degree of noise abatement, the precise selection and arrangement of materials for the partitions becomes part of a critical decision.
Consider for example the three pound per cubic foot density of fiberglass costs more than twice what a 1.5 pound per cubic foot density costs for the same volume of material, yet offers only a slight increase or improvement in noise abatement properties and the same Noise Reduction Coefficient (NRC). The principal reason for use of the higher density fiberglass is obviously not for noise abatement, but rather for rigidity. The following table illustrates the minor increase in noise-absorption properties due to increased density:
______________________________________ Absorption Coefficients at Octave Frequencies Density 250 500 1000 2000 NRC ______________________________________ 1.5 lbs/ft.sup.3 0.54 0.76 0.83 0.87 75 (1 inch thick) 3.0 lbs/ft.sup.3 0.49 0.69 0.87 0.92 75 (1 inch thick) ______________________________________
Another design variation for acoustical partitions and one which is commonly used is to employ fiberglass in conjunction with a rigid septum such as steel. In this type of construction, a lower density of fiberglass can be used and adequate rigidity can still be maintained. However, the septum can be very expensive, especially if constructed of steel.
In order to deal with what is seen as drawbacks and shortcomings of currently designed acoustical partitions, the present invention has been conceived. The present invention provides excellent rigidity and noise abatement properties without the corresponding high cost (expense) associated with a high-density fiberglass core or septum. This result is achieved by creating a core of sound-absorbing material fabricated from a plurality of sheets of material laminated into a core panel. These laminated sheets may be of the same material but with two different densities and are alternately sequenced in order to create the acoustical core for the partition. Alternatively, the sheets of material may be of two different materials, such as one insulating material and a chip board (or particle board material), and alternated in the lamination for the core. A third option is to do either of the above where the two types of material that are in alternating sequence have different thicknesses. The design concepts and variations of the present invention provide designers with a much greater degree of flexibility in efficiently abating specific types of noise and/or specific frequencies of sound.
There is a spin-off benefit of the present invention with regard to the method of manufacture. Fiberglass and foam insulation which is fabricated in panel form is typically sized into standard widths, such as 48 inches, which is common for three-pound density fiberglass board. If a 30-inch width of core material is required by the acoustical partition manufacturer, the 18 inches which remain initially represent wasted material which in effect increases the cost of the 30-inch panel which is used. Presumably, two 18-inch pieces could be cut down to 15 inches and then joined together for a 30-inch wide panel, but the special nature of this procedure in a shop which is geared to producing 48-inch panels or using 30-inch panels creates manufacturing inefficiencies. The resultant acoustical panel would not have the requisite fit, rigidity or structural integrity which is desired for acoustical partitions.
In the present invention, the standard width panels are stacked side by side on edge and in abutting relationship and a layer approximately the same thickness as the acoustical partition frame is cut from the top of this stacked block of standard-width panels. If each panel is, for example, one inch in thickness, then for a 30-inch width panel for the partition, 30 standard-width panels are stacked on edge. When the cut is made, the only waste is of the saw blade thickness as it cuts through the material. In the described method, if 48-inch panels are used, this 48-inch dimension will in effect be a height dimension for the block of standard-width panels which are abutted together. As successive layers are cut from the top of this panel block, each layer is cut at the desired thickness so as to match the partition frame in which the panel will be placed. The only loss as mentioned is due to the saw blade width and if a 48-inch panel is cut in 1-inch strips by a 1/16-inch thick saw blade, 45 panels will be produced allowing three inches for losses, 2.94 inches of which will be due to the blade thickness.
While a variety of designs exist for acoustical panels, none anticipate or suggest the present invention. Further, it would not be obvious to a person having ordinary skill in the acoustical partition art to combine structural portions from a plurality of references in order to create the present invention. Nonetheless, some of the structural aspects of these partitions may be of interest relative to the present invention, if for nothing more than to illustrate the substantial differences between the present invention and what is disclosed in such references. Consequently, the following list of patent references is provided as being representative of the type of acoustical panels found in the art:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,630,416 Lapins et al. 12/23/86 4,167,598 Logan et al. 9/11/79 4,076,100 Davis 2/28/78 3,949,827 Witherspoon 4/13/76 3,274,046 Shannon et al. 9/20/66 ______________________________________
Lapins et al. discloses a movable, prefabricated wall panel having a rigid rectangular frame. A core structure is disposed in the region bounded by the frame which core structure preferably comprises at least one honeycomb layer. Sheet-like skins are fixedly secured to opposite sides of the frame and extend across the region bounded by the frame for confining the honeycomb layer therebetween. Each sheet-like skin is covered by a layer of porous fiberglass material for absorbing sound, and this layer includes an inner thin mat of high-density fiberglass which is in turn covered by relatively thick outer layer of low-density fiberglass. This outer layer has a variable density gradient across the thickness thereof which density gradient progressively increases across the thickness.
Logan et al. discloses a heat and sound insulating panel assembly for a wall, ceiling or floor construction and consists of a plurality of interlocking vacuum-chamber panel elements fabricated from a relatively hard, low thermally conductive fire-resistant or fireproof material with heat-reflective, moisture-restraining coatings on its inner and outer surfaces. Abutting surfaces may be provided with sound-cushioning pads, and vacuum-chamber spacer column elements may be employed, interlocked between panel elements for uniform increased panel wall thickness.
Davis discloses an oil-impervious acoustical board formed of fire-retarding materials which has the properties of being fire-retardant, sound-absorbing, heat insulating and decorative. This acoustical board may be formed in virtually any size and shape and is composed of fiberglass reinforced melamine resin panels having one grooved surface covered by fiberglass cloth with perforations suitable to admit sound waves into the grooved areas of the underlying board. The sound waves which are admitted are intended to be trapped by the design of the acoustical board.
Witherspoon discloses an acoustical panel assembly having improved structural, decorative and acoustical properties wherein the panel includes a perimeter frame, a thin septum member supported in the center of the frame and a fibrous glass layer positioned adjacent each side of the septum member. A molded, semi-rigid fibrous glass diffuser member is positioned adjacent each of the fiberglass layers. This assembly includes means for joining adjacent panel assemblies and, in one embodiment, an outer decorative fabric layer positioned adjacent each of the outer surfaces of the diffuser members.
Shannon et al. discloses a combined fiber and cellular panel including a plurality of bodily separate masses of intermeshed vitreous fibers which masses are disposed in closely adjacent, side-by-side relationship. The fibers in the masses are bonded to one another at points of contact by a binder material. In one embodiment of this device, there is a honeycomb core pattern disposed between a pair of spaced parallel skins. Also disclosed in this patent reference is a procedure or method of fabrication involving creation of a laminar structure composed of 24 phenolformaldehyde bonded glass fiber boards interspersed with 23 layers of novolac composition. The resultant structure is then cut into 24 slices, each slice approximately one inch thick and each cut was parallel to an edge of one of the boards and perpendicular to a major surface thereof.
As mentioned, although there are some features of the foregoing references which may be of interest with regard to the present invention, there are substantial differences between the present invention and what is disclosed by these references, all of which will be apparent from the following descriptions.